from heapq import *
N=int(input())
R=list(map(int,input().split()))

dist = [N]*N
dist[0] = 0
que = [(0,0)]

for i in range(N):
    d,rr = que[0]
    while i>rr:
        heappop(que)
        d,rr = que[0]
    dist[i] = d
    if i+1<N:
        r = R[i]
        heappush(que, (d+1,r-1))
print(dist[-1])